1. Field of The Invention
The present invention relates to a control system for an excavator, and more particularly to a system for automatically controlling quantity of hydraulic fluid of the excavator in which main hydraulic pumps thereof are automatically control led in order to output optimal quantity of the hydraulic fluid outputted therefrom to a swing motor during a swinging operation, and also output minimum quantity of hydraulic fluid therefrom to actuators in case of an overload occurring on the actuators.
2. Description of the Prior Art
Conventionally, known excavators are provided with a plurality of actuators which are actuated by hydraulic power and comprise a driving motor section comprising a swing motor for swinging an upper frame including a control cab with respect to a lower frame provided with travelling members, such as crawlers, and travel ling motors for travelling the excavators, and an actuating cylinder section comprising a dipper cylinder for driving a dipper stick, a boom cylinder for driving a boom and a bucket cylinder for driving a bucket. The above actuators are controlled by virtue of manipulating control levers/pedals provided in the cab and manipulated by the operator in order to efficiently carry out several operations of the excavator such as excavating operations, surface finishing operations, loading operations and the like.
However, the known excavators have the following disadvantages resulting in fatigue of the operator in order to deteriorate the operational effect of the excavator, and causing the operational energy to be unnecessarily lost.
First, the excavator often carries out the swinging operation in which the swing motor is driven by virtue of manipulation for the swing lever, thereby swinging the upper frame with respect to the lower frame. At this time, a main hydraulic pump connected to a directional control valve of the swing motor outputs, in accordance with a control signal outputted from a controller, the quantity of hydraulic fluid to the swing motor by way of the directional control valve. Here, as the swing motor control lever is manipulated, the quantity of the hydraulic fluid outputted from the main pump to the swing motor is varied as described at the characteristic curves of a graph of FIG. 5.
Referring to the graph, it is known that as the swing motor control lever is manipulated, the main pump outputs considerable quantity of the hydraulic fluid to the swing motor before the upper frame of the excavator swings with respect to the lower frame so that the quantity of the hydraulic fluid represented at the deviant lines of the graph is lost, thereby causing the operational energy to be lost. The reason why the main pump outputs considerable quantity of the hydraulic fluid to the swing motor before starting of the swinging action of the swing motor is that upon receiving respective control signals from the controller at the same time, the swing motor can not swing the upper frame of the excavator with respect to the lower frame due to weight of the upper frame but the main pump outputs at once the required quantity of the hydraulic fluid to the swing motor.
Therefore, the operator has to minutely manipulate the swing control lever in order to control the outputting operation of the hydraulic fluid of the main hydraulic pump to correspond to the practical swinging operation of the swing motor as described at the characteristic curves of the graph of FIG. 5, so that the hydraulic fluid outputted from the main pump is not unnecessarily lost.
However, it is required great skill for the operator to control the swing operation of the excavator not to dissipate the hydraulic fluid. In result, the known excavators have a disadvantage in that such a minute operation causes fatigue of the operator in a long time operation, thereby causing the operational effect of the excavator to deteriorate, and a safety accident to occur during the swinging operation. In addition, the known excavators have another disadvantage in that the minute swinging operation for preventing operational energy loss can not be carried out completely even by a skilled operator so that a part of quantity of hydraulic fluid is unnecessarily lost as before.
Second, the known excavator is equipped, as described above, with a plurality of actuators, such as the travelling motors, the cylinder actuators and the swing motor. The known excavator is also provided with the main hydraulic pumps for supplying the hydraulic fluid for the actuators in order to drive them. However in case of occurrence of overload on the actuators, the actuators automatically stop their operations at once, while the main hydraulic pumps continuously output hydraulic fluid to the actuators. In result, the hydraulic fluid continuously outputted from the main pumps to the actuators is not used for driving the actuators as the actuators stop their operations due to the overload occurring thereon but directly drains into a drain tank, thereby causing the main hydraulic pumps to be unnecessarily driven by the engine. Therefore, the known excavators have a disadvantage in that in case of occurring an overload on an actuator, resulting in stopping the operation thereof, the driving power for driving the engine to continuously drive the main pumps is unnecessarily dissipated. SUMMARY OF THE INVENTION
Therefore, the present invention is accomplished in order to overcome the above disadvantages.
It is an object of the present invention to provide a system for automatically controlling quantity of hydraulic fluid of an excavator in which in case of swinging operation for driving a swing motor in order to turn an upper frame of the excavator with respect to a lower frame thereof, a hydraulic pump is automatically controlled by an electric controller in order to optimally output hydraulic fluid to timely correspond to starting of a practical swinging operation of the swing motor, thereby reducing a hydraulic fluid loss as possible as, and accomplishing a smooth and rapid swinging operation by a simple manipulation for a swing motor control lever without occurrence of mechanical shock on the main pump or the swing motor.
It is another object of the present invention to provide a system for automatically controlling quantity of hydraulic fluid of an excavator in which in case of sensing a relatively slower operational speed of an actuator which is lower than 1/2 speed of a minimum operational speed Vain of the actuator occurring when the actuator is supplied with a minimum quantity of the hydraulic fluid from the main hydraulic pumps, the electric controller outputs a control signal of a minimum current value to wobbling angle control valves of the main hydraulic pumps in order to minimize the wobbling angles of the wobbling plates of the main hydraulic pumps so as to minimize the quantity of the hydraulic fluid outputted from the pumps to the actuator, while in case of sensing a returnable speed of the actuator which is higher than 3/4 speed of a minimum operational speed Vmin of the actuator, thereby causing the driving power for driving an engine to be efficiently prevented from being lost due to an overload occurring on the actuators.
In one aspect, the above objects of the present invention can be accomplished by providing in an apparatus for automatically controlling quantity of hydraulic fluid of an excavator comprising a plurality of actuators comprising a boom cylinder for actuating a boom, a dipper cylinder for actuating a dipper stick, a bucket cylinder for actuating a bucket, a swing motor for swinging an upper frame of the excavator with respect to a lower frame thereof and travelling motors for travel ling said excavator; an electronic controller for controlling the operation of said actuators; main hydraulic pumps for supplying hydraulic fluid for said actuators; a sub-hydraulic pump for supplying pilot hydraulic fluid; a plurality of directional control valves each connected to said main hydraulic pumps and said electronic controller for controlling operational direction of said actuators and also quantity of said hydraulic fluid flow; pilot valve blocks adapted to controllably move spools of said directional control valves in accordance with electric control signals outputted from said electronic controller; wobbling angle control valves disposed between the controller and the main pumps for controlling wobbling angles of the main hydraulic pumps in order to control said quantity of hydraulic fluid flow outputted therefrom; positional sensors provided at respective actuators in order to sense positional displacement values of said actuators; control levers/pedals for outputting respective electric signals corresponding to handling values for actuators to the controller; and a plurality of amplifiers disposed among the controller and said pilot valve blocks and said wobbling angle control valves; respectively, for amplifying electric signals outputted from said controller to said pilot valve blocks and said wobbling angle control valves; said controller comprising: a CPU for processing input analog signals in order to output control signals; an analog/digital signal converter for converting the input analog signals corresponding to manipulation values applied from the control levers/pedals to the controller into digital signals; an analog/digital signal converter/counter for converting and counting an input signal corresponding to a swinging positional value of the swing motor applied from a positional sensor of tile swing motor; first and second digital/analog signal converters for converting digital control signals from the CPU into analog control signals for controlling the spools of the directional control valves of the actuators in accordance with the manipulating values of the control levers/pedals; a third digital/analog signal converter for converting digital control signals from the CPU into analog control signals for additional output quantity of fluid flow and target output quantity of fluid flow; and signal amplifiers electrically connected to the digital/analog signal converters, respectively.
In another aspect, the above objects of the present invention can be accomplished by providing in an excavator comprising actuators including a boom cylinder for actuating a boom, a dipper cylinder for actuating a dipper stick, a bucket cylinder for actuating a bucket, a swing motor for swinging an upper frame of the excavator with respect to a lower frame thereof and travelling motors for travelling said excavator, a control process for automatically controlling a control apparatus for controlling the quantity of hydraulic fluid of the excavator comprising an electronic controller for controlling the operation of said actuators; main hydraulic pumps for supplying hydraulic fluid for said actuators; a sub-hydraulic pump for supplying pilot hydraulic fluid; a plurality of directional control valves each connected to said main hydraulic pumps and said electronic controller for controlling operational direction of said actuators and also quantity of said hydraulic fluid flow; pilot valve blocks adapted to controllably move spools of said directional control valves in accordance with electric control signals outputted from said electronic controller; wobbling angle control valves disposed between the controller and the main pumps for controlling wobbling angles of the main hydraulic pumps in order to control said quantity of hydraulic fluid flow outputted therefrom; positional sensors provided at respective actuators in order to sense positional displacement values of said actuators; control levers/pedals for outputting respective electric signals corresponding to handling values for actuators to the controller; and a plurality of amplifiers disposed among the controller and said pilot valve blocks and said wobbling angle control valves; respectively, for amplifying electric signals outputted from said controller to said pilot valve blocks and said wobbling angle control valves; the control process further comprising the steps of: upon receiving a manipulation value from the control levers/pedals, determining whether the manipulation value for the control levers/pedals is only for the swing motor in order to perform a swinging operation; upon receiving a swing positional value of the swing motor from the swing motor positional sensor, calculating a target output quantity of fluid flow of the main hydraulic pump in accordance with the manipulation value of the swing motor control lever, and calculating a practical quantity of hydraulic fluid flow of the main pump on the basis of the swing positional value of the swing motor, thereafter comparing the target output quantity of the fluid flow with the practical quantity of the fluid flow in order to calculate a difference therebetween; and upon determining whether the difference is not zero, calculating an additional output quantity of fluid flow for the practical quantity of the fluid flow and an additional target output quantity of fluid flow in order to satisfy a desired swing operation according to the manipulation values of the swing lever control lever, thereafter outputting an electric control signal corresponding to the additional target output quantity of fluid flow to the wobbling angle control valve of the main hydraulic pump.
In still another aspect, the above objects of the present invention can be accomplished by providing a control process comprising the steps of: upon receiving operational speed of an actuator from a positional sensor thereof, determining whether the actuator is normally driven; if the actuator is not normally driven, determining whether the operational speed of the actuator is not exceeding 1/2 speed of a minimum operational speed of the actuator, said minimum operational speed occurring when the actuator is supplied with a minimum quantity of the hydraulic fluid from the main hydraulic pump; if the operational speed of the actuator is not exceeding the 1/2 speed of the minimum operational speed, outputting a minimum current value to the wobbling angle control valve in order to minimize the wobbling angle of the main pump, thereby making the main pump to output a minimum quantity of fluid flow to the actuator; if the actuator is normally driven, determining whether the operational speed of the actuator is equal to or exceeds 3/4 speed of the minimum operational speed of the actuator; and if the operational speed of the actuator is equal to or exceeds the 3/4 speed of the minimum operational speed, outputting an electric control signal to the wobbling angle control valves in order to allow the main pumps to output quantity of fluid flow according to the manipulation values of the control levers/pedals.